Yes i've had brake calipers stick and seize. I doubt the ABS has anything to do with it. The pistons get a little dirty inside, or have old fluid, or the caliper seals swell just a little and the piston can stick. Remember that normal rotor runout is the only thing that retracts the pads on the Camry, there are no return springs on Camry calipers. (Most cars DO NOT have return springs on their disc brakes, the only exception i ever saw was Ford Escort last generation)
There's usually some warning before this happens, usually it doesnt happen so fast as it did to your Camry. Like when you inspect the brakes, the pads are more worn on one side.
Flushing helps to prevent this, but is not a perfect solution. Because when you flush the fluid (however its done, doesnt matter) some dirty fluid always remains in the bottom of the calipers and wheel cylinders. So unless you take everything apart and clean it there will always be a little bit of dirty fluid in your system.
$550 to fix two calipers? Thats alot but not unfair, it would be much cheaper to do it yourself if feasible. Napa online has some good ones but you may find it cheaper.
http://www.napaonline.com/masterpage...oaded)+-+Remfd.